What do you think of out and ref in C#? Explore the differences between them

When learning C#, you will always encounter some language commands and the like that have similar but different usages. Today we are discussing the difference between out and ref in C#. First, we will discuss the usage of each. , below I will summarize the difference between out and ref. apache php mysql

Both are passed by address, and the values ​​of the original parameters will be changed after use.

ref can pass the value of the parameter into the function, but out needs to clear the parameter, which means that you cannot pass a value from out. After out enters, the value of the parameter will be empty, so you must Initialize once. This is the difference between the two, or as some netizens said, ref means both in and out, while out means only going out but not going in.

ref (C# reference) The

ref keyword causes parameters to be passed by reference. The effect is that when control is passed back to the calling method, any changes to the parameters in the method will be reflected in the variable. To use ref parameters, both the method definition and the method call must explicitly use the ref keyword.

For example:

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class RefExample { static void Method(ref int i) {         i = 44; } static void Main() {         int val = 0;         Method(ref val);         // val is now 44 } }

The parameters passed to the ref parameter must be initialized first. This is different from out , whose arguments do not need to be explicitly initialized before being passed.

Although ref and out are handled differently at runtime, they are handled the same way at compile time. Therefore, if one method takes a ref parameter and another method takes an out parameter, both methods cannot be overloaded. For example, the two methods in the following code are identical from a compilation perspective, so the following code will not compile:

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class CS0663_Example { // Compiler error CS0663: "cannot define overloaded // methods that differ only on ref and out". public void SampleMethod(ref int i) { } public void SampleMethod(out int i) { } }

However, if one method takes ref or out parameters, and another method does not take these two parameters, it can be overloaded, as shown in the following example:

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class RefOutOverloadExample { public void SampleMethod(int i) { } public void SampleMethod(ref int i) { } }

out (C# Reference) The

out keyword causes parameters to be passed by reference. This is similar to the ref keyword, except that ref requires that the variable must be initialized before being passed. To use out parameters, both the method definition and the method call must explicitly use the out keyword.

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class OutExample { static void Method(out int i) {         i = 44; } static void Main() {         int value;         Method(out value);          // value is now 44 } }

Although variables passed as out parameters do not have to be initialized before passing, the method needs to be called so that it can be assigned a value before the method returns.

ref and out keywords are handled differently at runtime, but the same way at compile time. Therefore, if one method takes a ref parameter and another method takes an out parameter, both methods cannot be overloaded. For example, the two methods in the following code are identical from a compilation perspective, so the following code will not compile:

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class CS0663_Example { // Compiler error CS0663: "Cannot define overloaded // methods that differ only on ref and out". public void SampleMethod(out int i) { } public void SampleMethod(ref int i) { } }

However, if one method takes ref or out parameters, and another method does not take these two types of parameters, it can be overloaded as follows:

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class RefOutOverloadExample { public void SampleMethod(int i) { } public void SampleMethod(out int i) { } }

The following is what I compiled based on my experience:

Difference

The difference between ref and out In C#, parameters can be passed by value or by reference . Passing parameters by reference allows function members to change the parameter's value and retain that change. To pass parameters by reference, use the ref or out keyword. Both the ref and out keywords can provide similar functions and function much like pointer variables in C. The difference between them is:

1. When using ref type parameters, the parameters passed in must be initialized first. For out, it must be initialized in the method.

2. When using ref and out, you must add the Ref or Out keyword in the parameters of the method and when executing the method. to satisfy the match.

3. Out is suitable for use where retrun requires multiple return values, while ref is used when the called method needs to modify the caller's reference.

The out method parameter keyword on a method parameter causes the method reference to be passed to the same variable of the method. Any changes made to the parameters in the method will be reflected in this variable when control is passed back to the calling method.

Declaring an out method is useful when you want the method to return multiple values. Methods using out parameters can still return a value. A method can have more than one out parameter.

To use out parameters, the parameters must be passed explicitly to the method as out parameters. The value of the out parameter is not passed to the out parameter.

Variables passed as out parameters do not have to be initialized. However, the out parameter must be assigned a value before the method returns.

Properties are not variables and cannot be passed as out parameters.

In short, it can be summarized in one sentence: ref means both in and out, while out means only going out but not going in.

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